The present invention relates to data center infrastructure and usage, and more particularly, this invention relates to a quantized congestion notification (QCN) extension to Explicit Congestion Notification (ECN) for transport-based end-to-end congestion notification.
Data Center Transmission Control Protocol (DCTCP) was created in 2010 and is a prevalent data center transport and TCP Incast/Hadoop solution, which is currently adopted by many standards organizations and companies, such as the Internet Engineering Task Force (IETF), Linux, Microsoft, Cisco, etc.
DCTCP uses a modified Random Early Detection (RED)/ECN feedback and a multi-bit feedback estimator that filters incoming single-bit ECN streams. This compensates the halving of the TCP congestion window (partly similar to QCN's reaction point) with a smooth congestion window (cwnd) reduction function, reminiscent of QCN's rate decrease, hence departing from TCP's halving of the cwnd.
DCTCP reduces flow completion times (FCTs) on average by about 29%; however, since DCTCP is deadline-agnostic, DCTCP also misses about 7% of the deadlines. Also, DCTCP surreptitiously attempts to mimic not only QCN reaction point (RP) behavior (it has a smoother reaction than TCP's halving of the cwnd), but also the multi-bit QCN congestion point (CP) feedback, which is derived from the congestion notification message (CNM) 6b congestion Fb, as inferred from timeseries of sparse, single-bit ECN marking streams.
Now, relating to QCN, but not DCTCP, TCP Incast in a QCN-enabled lossy network has a problem where the process may actually result in the loss of some information, which may be in conflict with a default assumption of lossless Converged Enhanced Ethernet (CEE).